the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Feb 2026
Case Studies on Mesospheric Fronts at Low Latitudes over Brazil
Abstract. This study investigates four mesospheric front events observed over Cachoeira Paulista (23° S, 45° W), Brazil, between 2007 and 2008, using coordinated measurements from an all-sky airglow imager, meteor wind radar, and sodium temperature lidar. The events, recorded on 14–15 September 2007, 5 October 2007, 31 March 2008, and 3 September 2008, were classified as mesospheric bores, two undular and two turbulent based on airglow morphology and atmospheric background structure. Vertical profiles of wind and temperature, along with vertical wavenumber diagnostics, revealed the presence of thermal and thermal-Doppler ducts supporting the bores. Classical complementary emission responses were observed in single-duct environments, while multi-duct layering led to complex airglow signatures, including mixed bright and dark fronts. This is the first study in Brazil’s low-latitude region to employ simultaneous multi-instrument observations for mesospheric bore analysis, offering new insights into duct dynamics, emission behavior, and wave–duct interactions in the mesosphere and lower thermosphere.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Annales Geophysicae.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-6569', Anonymous Referee #1, 10 Mar 2026
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RC2: 'Comment on egusphere-2025-6569', Anonymous Referee #2, 14 Mar 2026
This study examines mesospheric wave front events observed using an all-sky camera in Brazil. A notable advantage of the dataset utilized in this research is its integration with height-resolved temperature and wind measurements obtained from a sodium LIDAR and a meteor radar, respectively. The duct structure has been assessed by estimating the square of the vertical wavenumber (m^2), and the occurrence of the bright/dark front has been discussed in relation to the relative location of the optical emission layer to the duct structure. However, it is important to note that the conclusions regarding the appearance of the bright/dark front are based on assumptions about the emission altitudes. While Section 4 presents some general topics related to the wave front, the article does not include a section dedicated to discussing causality in producing measurements. It would be beneficial to address these two aspects for publication. Additionally, there are several minor comments that could be considered.
[Major comments]
1. This study considers emission altitudes for the three optical wavelengths as 87, 94, and 97 km for OH, O2, and 557.7 nm, respectively. Under this assumption, this study explains that the emission intensity at the wave front may decrease or increase depending on whether the emission altitude is above or below the duct structure. Based on this concept, the study seeks to understand the optical camera measurements from the four analyzed events. While measurements such as sodium LIDAR temperature and MTR wind velocity are utilized to infer the duct structure, it is important to note that the emission altitude is hypothetical. In other words, one of the crucial pieces of information for drawing the conclusions of this study relies on the hypothesis. This could be considered a less robust foundation for the physical explanation. If there is a significant error in the hypothesis, it might fundamentally affect the results of this study. The authors should consider this point, and I would recommend revising the text in light of these comments.
1-1. Please address the following issues in a new "Discussion" section following Section 3.
1-2. In the section established in 1-1, it would be greatly appreciated if multiple references could be included to substantiate the assumption regarding the emission altitudes. To ensure a comprehensive perspective, it might be beneficial to reference as many sources as possible, thereby avoiding the impression of selectively citing literature that aligns conveniently with this study. It is important to consider that merely citing studies that assume the same emission altitude as this study does may not provide sufficient support for this study, as those studies only make similar assumptions. Valuable information can be derived from emission altitudes based on observations or simulations grounded in physical or chemical principles.
1-3. The emission altitudes proposed in various references may differ. It would be helpful to discuss in the newly created section (1-1) how this variability might affect the conclusions of this study.
1-4. In the newly created section (1-1), it would be beneficial to examine whether the emission altitude could fluctuate due to the special events or wave fronts, and if so, to what extent, and what impact this might have on the conclusions of this study.
2. Could the authors explain the mechanism by which the emission intensity at the wave front varies with the relative height of the duct and the altitude of the airglow emission? Specifically, it would be helpful to understand why the same wave structure is observed in camera images of the emission layer measured outside the duct, considering the concept that atmospheric waves propagate through the duct, meaning they propagate horizontally while reflecting off the upper and lower planes of the duct.
3. It is important to note that the sodium LIDAR and MTR used to estimate duct altitude differ significantly in temporal resolution and field of view. The former is considered to capture smaller scale phenomena both temporally and spatially compared to the latter. Additionally, the temporal and spatial measurement scales of each instrument are likely to differ relative to those of the atmospheric waves under study. When comparing the altitude profiles of temperature and wind velocity (e.g., Figures 2a and 2c), finer fluctuations are more distinctly visible in the temperature profile or the LIDAR measurement. This may be attributed to differences in measurement methods. Such differences may also impact the m^2 altitude profile (e.g., Figures 2e and 2f), potentially leading to an underestimation of the m^2 wind term. I would be grateful if you could discuss these points comprehensively in the new section established in 1-1.
[Minor comments]
L76: Include the optical wavelength for O2.
L78: What is the sequence for measuring the three optical wavelengths?
L79: It would be preferable to write “670 x 650” to maintain consistency with the order of 1340 x 1300 in L74.
L103: Does “the wind” refer to “the wind effect”?
L107-109: Please explain the rationale behind classifying the information obtained from these three optical wavelengths.
L124: Besides “signal-to-noise ratio,” what constitutes “image quality”? Please specify in the text.
L138: Event 4 > Event 3
L138: Event 3 is the longest observed event, lasting over an hour, while the other events are brief (20, 43, and 14 minutes). Could this discrepancy introduce bias in period identification?
Table 1: Are the dates based on the evening when the optical measurement began, or when the event was detected? Special attention is needed for the presentation of Event 1.
L150: The time zone listed as Local Time in Table 1 is inconsistent. Please verify. Similar comments apply to other events.
L151: from northwest to southeast (NW-SE) > southeastward
Figure 3: Since it mentions "Mid-plane," the horizontal axis of the graph likely represents horizontal distance rather than time. Is this interpretation correct? In any case, please specify what the horizontal axis represents on the graph.
Figure 3: Does the emission altitude not oscillate vertically due to the ducted wave?
L200: from northwest to southeast > southeastward
L222-223: “Moreover, the narrow width … gravity wave propagation.” Could you explain the reasoning behind this statement in the text?
L242: from northwest to southeast > southeastward
L280: from southwest to northeast > northeastward
Figure 8: Event 5 > Event 4
L329-331: Can you identify any corresponding wave patterns in the O2 and OI images?
L383-385: The image data analyzed in this study is not available on this webpage.
Citation: https://doi.org/10.5194/egusphere-2025-6569-RC2
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- 1
This paper describes four bore-like wave events observed in the mesosphere with an all-sky imager over South-East Brazil. A complete description of the atmospheric background conditions was also provided by coincident Na lidar and radar measurements. Bore-like events are trapped waves which are able to propagate over large distances. Their presence gives important information about the structure of the upper atmosphere.
The manuscript is clear and well-written. Although it provides some interesting results, these are not new. They just corroborate previous studies.
The paper gives a good overview of ducted waves science and a fairly complete description of the four investigated cases. However, the authors should answer the following comments/questions:
- A map illustrating the measurements would be useful, with the field of view of the imager and the locations of the Na lidar beams where they intersect the OH layer.
- How was Lh measured because the events all appeared as a single front?
- In equation (1), only some of the parts are used in this study, why is that? What about 1/4H2 and u'?
- Uncertainties are plotted on the figures, can you also provide the error calculations?
- Evidence for inversion layers is not always obvious, especially for events 2 and 4. It would be interesting to expand the background plots to the whole nights. Something similar to Figure 7 in Bossert et al., 2014 (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014JD021460). It would also help providing an explanation for the origin of the ducting regions (large scale wave, tide?), and interpret the data, not just present it.
- Some figures could be nicer, especially 2, 5, 7, and 9, which look low quality.
Minor edits:
l. 83: I think SJC is west of Cachoeira Paulista!
SABER is mentioned in the data availability section but it's not clear when/how it was used in the study.